Comparison of the transport properties of normal and expanded forms of a cation-exchange membrane. Part 2.—Self-diffusion and electrical properties of membranes in the sodium form in concentrated sodium chloride

Abstract

The influence of shrinking and increasing salt uptake on the transport properties of normal and expanded membranes has been examined. Isotopic diffusion coefficients from sodium and chloride ions were found to be functions of changing tortuosity and membrane electrolyte molality. Tortuosity corrected coefficients agreed closely with those of sodium and chloride ions in aqueous sodium chloride at equal molalities. Diffusion coefficients for tritiated water were constant, when corrected for tortuosity, and equal to the diffusion coefficient of tritiated water in pure water. From electrical measurements, it is shown that the ratio of solvent-fixed velocities of sodium and membranesulphonate ions is constant over the experimental range of conditions. The sulphonate ion is more mobile than sodium on this frame of reference and similar in behaviour to chloride or nitrate in free aqueous solution. All data indicate the validity of a simple aqueous model for membrane transport phenomena.